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The Forefront of Space Science

Planetary Plasma Environment and Atmospheric Outflow to be Elucidated by Extreme Ultraviolet Spectroscopy
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To achieve scientific goals

The key to achieving the above research objectives of planetary plasma environment and atmospheric outflow is to conduct optical observation with finer angle resolution than the planetsEapparent diameter. As the maximum apparent diameter of Jupiter and Venus is approx. 50 and 60 arcsecond respectively, we set angular resolution at ±5 arcsecond for this mission. Fig. 2 shows angle of field of the spectroscopic observation by extreme ultraviolet of Jupiter and Venus at that resolution. For successful observation, it is critical to stabilize satellite attitude with the same accuracy.

Figure 2
Figure 2. Observation examples of Jupiter (upper) and Venus (lower)
The Jupiter image is a synthetic one made from Io Plasma Torus observed by Saturn-explorer satellite Cassini and Jupiter’s polar aurora observed by both the Hubble Space Telescope and X-ray astronomical satellite Chandra. The Venus image is produced by computation simulation (Terada et al., 2009). Light blue frame corresponds to about 1 pixel size.

On our small scientific satellite, we have adopted an unconventional development approach. We are developing the satellite system (i.e., bus part) and observation instruments (i.e., mission part) separately to provide functions unique to the mission. After completing the development, we will integrate the two parts into a single satellite. This approach requires strict definition of the interface conditions between the bus and mission parts, but keeps the development scale small while assuring development efficiency and design flexibility of each part.

If we set the high-accuracy altitude stability ±5 arcsecond as the satellite-system requirement and fulfill it only by attitude-control system of the bus part, we must develop an ultra-high accuracy attitude-control system. For this problem, we determined to add an original interface that transmits planetary-position data in the observation view from the mission part to the attitude-control system in the bus part. A view guide camera (unnecessary for planetary spectroscopic observation) will be installed on the mission part too, eventually adding a planetary-tracking function to the attitude-control system. This adds to developmental requirements in both bus and mission parts, but allows us to ensure efficiency in overall satellite development. One of ISAS’s unique strong points, i.e. all-in-one development organization including both science and engineering, is working well to optimize the overall satellite development.

Toward further challenges

With SPRINT-A, we will tackle unresolved issues on the energy-transport process in the Jovian atmosphere and measurement of the dissipative amount of the atmosphere occurring around Venus and Mars. To understand the properties of magnetospheres and atmospheres under different environments from the earth’s leads us to reaffirm again the irreplaceable earth environment. We expect that our mission will also lead to understanding of the formation, birth and evolution of the solar system and planetary systems beyond. We will be delighted if the project triggers further thought about whether a planetary environment nurturing life such as the earth is consequential or incidental, and about fundamental questions on the life form called mankind.

Acknowledgment: To conduct the project, we have received a great deal of cooperation and support from a number of parties, not only project members. I would like to take this opportunity to express our sincere gratitude.

References: Spectroscopy Research, Onaka 1970, Yuseijin, Yoshikawa et al. 2012


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